# Comparative Assessment of Soil Organic Carbon Stocks in Sal (Shorea robusta) and Mixed Hardwood Forests of the Nepal Terai

## TL;DR

This study compares soil carbon storage in two forest types in Nepal, finding that mixed hardwood forests store more carbon than Sal-dominated forests.

## Contribution

The study quantifies the impact of forest composition on soil organic carbon stocks in the Nepal Terai, providing data for climate change mitigation strategies.

## Key findings

- Mixed hardwood forests stored significantly more soil organic carbon (18.25 t ha−1) than Sal forests (15.35 t ha−1) in the top 30 cm of soil.
- Bulk density was lower in mixed hardwood forests, and soil carbon concentration decreased with depth in both forest types.
- The topsoil (0–10 cm) contained the largest proportion of total soil organic carbon stock in both forest types.

## Abstract

Forest soils are a critical component of the global carbon cycle, yet the impact of forest composition on soil organic carbon (SOC) stocks in tropical regions remains poorly quantified. Understanding the differences between mono‐dominant and mixed‐species forests is essential for climate change mitigation strategies. This study provides a comparative assessment of SOC stocks in two major forest types of the Nepal Terai: Sal (
Shorea robusta
) mono‐dominant forests and Terai Mixed Hardwood (TMH) forests. Soil samples were collected from three depth intervals (0–10, 10–20, and 20–30 cm) in five replicate plots for each forest type in Kapilvastu District. Bulk density was measured using the core method, and SOC was determined via the Walkley‐Black wet oxidation technique. SOC stocks were calculated and differences between forest types were analyzed using analysis of variance (ANOVA). The mean SOC stock in the top 30 cm was significantly higher (p < 0.05) in TMH forests (18.25 ± 1.2 t ha−1) compared to
S. robusta
forests (15.35 ± 0.9 t ha−1). Bulk density was significantly lower in TMH soils, while SOC concentration decreased significantly with depth in both forest types. The topsoil (0–10 cm) layer contained the largest proportion of the total SOC stock. The findings demonstrate that mixed hardwood forests in the terai Nepal store significantly greater amounts of soil carbon than
S. robusta
‐dominated forests. This suggests that forest composition is a key determinant of carbon sequestration potential. Conservation and promotion of mixed‐species forests should be prioritized in forest management and carbon incentive programs, such as REDD+, to enhance terrestrial carbon sinks and mitigate climate change.